A 35-year-old man with a history of tuberculosis on anti-TB therapy (rifampicin, isoniazid, pyrazinamide, ethambutol) presents with fever, widespread erythematous macules progressing to blisters and erosions involving 45% of body surface area, including the face, trunk, and extremities. Mucosal involvement is extensive (oral, ocular, and genital). Laboratory findings show leukocytosis (WBC 14,000/μL), elevated transaminases (AST 120 U/L, ALT 140 U/L), and mild thrombocytopenia (platelets 110,000/μL). What is the most appropriate immediate next step in management?